ssh-copy-id [-i [identity_file]] [user@]machine

#!/bin/bash
# -------------------------------------------------------------------------------
# Author:   Loya.Chen
# Description: Execute commands on multiple remote hosts at the same time.
# -------------------------------------------------------------------------------
set -e
Usage() {
  echo "Usage: $0 host1 host2 ... 'command'"
}
if [ $# -lt 2 ] ;then
  Usage
  exit 0
else
  cmd=${!#}
fi
logfile=$(mktemp)
i=1
success=0
failed=0
for ip in $@;do 
  if [ $i -eq $# ];then
    break
  fi
  ssh $ip $cmd &> $logfile
  if [ $? -eq 0 ];then
    #((success++))
    success=$(($success+1))
    echo -e "\n\033[32m$ip | success \033[0m \n"
    cat $logfile
  else
    ((failed++))
    echo -e "\n\033[31m$ip | failed \033[0m\n "
    cat $logfile
  fi
  ((i++))
done
echo -e '\n-------------------------'
echo -e "\033[32msuccess: $success | failed: $failed \033[0m"
echo '-------------------------'

$ bash vssh 10.0.0.11 10.0.0.12 'free -m'
10.0.0.11 | success 
       total    used    free   shared  buffers   cached
Mem:     2871    156    2715     0     8     36
-/+ buffers/cache:    111    2760
Swap:     2047     0    2047
10.0.0.12 | success 
       total    used    free   shared  buffers   cached
Mem:      980    615    365     0     12     69
-/+ buffers/cache:    533    447
Swap:     2047     0    2047
-------------------------
success: 2 | failed: 0 
-------------------------